In recent years, substantial innovations have been made in medical imaging that allow 3D reconstruction of highly detailed anatomical reproductions. Tomographic representations are now available from computerized axial tomography systems, positron emission tomography systems, and magnetic resonance imaging systems. These representations comprise, in essence, a set of contiguous sections or slices of an anatomical region. 3D reconstruction of biological structures from tomographic serial sections have become highly valued as diagnostic instrumentalities. One area of particular relevance for 3D reconstruction is neuroscience, in which the complicated internal structure of a brain is often impossible to visualize or analyze without the help of computer imaging methods. Due however to the masses of data required to be processed to reconstruct, manipulate and display 3D images, such images are not available on a real-time basis and may take anywhere from hours to days to construct using very powerful computers.
Recently, the quantitative analysis of brain images and brain function has been enhanced by the work of Chen et al., as reported in "Image Analysis of PET Data With the Aid of CT and MR Images", Information Processing in Medical Imaging, edited by DeGraaf et al., Plenum Press, N.Y., 1988, pp. 601-611. Therein is taught a method for overlaying tomographic PET studies onto either computerized tomography or magnetic resonance tomographic studies to enable not only neural structures to be visualized, but also neural function of various portions of the structure. The Chen et al. approach requires precise image correlations in three dimensions of the overlaid PET/MRI/CAT scans. As such, these correlations require positional adjustments of 3D images, one with respect to the other, until an optimum alignment occurs.
Notwithstanding the value of such studies, considerable processing time is required to translate and rotate the various images to achieve their accurate alignments. Because of the formidable computer tasks involved in achieving those alignments, such methodologies have been largely limited to a few laboratories with large resources for hardware and software.
A review of available three-dimensional imaging systems has recently been published, i.e., "Toward Computerized Morphometric Facilities: A review of 58 software packages for computer-aided three-dimensional reconstruction, quantification, and picture generation from parallel serial sections", Huijsmans, The Anatomical Record, Vol. 216, pp. 449-470 (1986). That review indicates that few systems are available which accommodate volume imaging and of those, all are extremely expensive.
Newly available powerful workstations have both substantial computing and random access memory capacities that provide many functions necessary for volumetric image reconstruction at moderate cost. However, interpolative operations incident to such reconstructions continue to pose a substantial problem for such work stations. An interpolative operation is one which occurs when an image is rotated by an oblique angle, translated by a non-integer offset or scaled by a non-integer factor, thereby requiring grey level adjustments to the pixels that represent the new, transformed image. In such workstations, oblique rotations, non-integer translation or non-integer scaling may require hours of central processing unit time for a 3D data set.
Another type of specialized video processor has also become available recently, applicable to a limited set of image processing applications. The Datacube Corporation, Peabody, Mass. produces a family of image processor boards called Max Video. Those processors are pipeline systems that perform special purpose, image processing functions extremely rapidly. As part of the Max Video family, Datacube markets a special purpose processor made up of three subassembly cards, an MAX-XFS card, an INTERPOLATOR card and an ADDGEN-1 card. In combination, those cards comprise a rotator assembly. The rotator assembly automatically rotates, by any prescribed angle, an image as it is being transferred from the first FRAMESTORE to the second FRAMESTORE. Those cards, together, are called a rotator set and in effect, comprise a pipeline processor which, in approximately 1/30th of a second, accomplishes a desired image rotation (including interpolation of gray values in neighborhoods of pixels to assure that the new pixel representation accurately represents the rotated image's grey values). Unfortunately, such limited function processors only have the ability to accomplish the image rotation in the image plane stored in the first frame store. As a result, while they are extremely fast in operation in that plane, they are incapable of operations in other image planes.
Accordingly, it is an object of this invention to provide an improved apparatus for the reorientation of 3D images and for the display thereof.
It is still another object of this invention to provide an inexpensive data processing apparatus adapted to reorient images in time frames comparable to much larger and more expensive data processing apparatus.
It is still another object of this invention to provide an improved method for the reorientation of 3D images, which method makes use of high speed functions in image processing apparatus, but avoids the use of less efficient image processing functions therein.